The difference between a short story and a novel is akin to the difference between a sharp cartoon and a busy landscape. Or Twist and Shout and The Emperor Concerto. They’re all significant but require different skills and talents to pull them off.
The Author’s novels were written with a story to tell. The Price of Redemption involves an elaborate crime that requires a full cast of characters on both sides of the Atlantic for it to unfold.
The story is more complex than can be fitted into (the typical) 15 pages of a short story. Similarly The Road To Givenchy requires several hundred pages to develop all its characters and interrelationships in 6 countries. It was written as a tribute to two great uncles killed in the First World War and required more detail than a short story could fit. The Author expects to write at least two more novels in the near future.